ANTIDYSRHYTHIMC Flashcards
Phase 0 of the myocytes
rapid depolarization (influx of Na due to opening of fast Na channels)
Phase I of the myocytes
partial repolarization inward Na current deactivated, outflow of K
Phase 2 of the myocytes
Plateau (slow inward of Ca2+ balanced by outward K+ current)
Phase 3 of the myocytes
repolarization (calcium current inactivates, K+ outflow)
Phase 4 of the myocytes
Resting membrane potential (Na+ efflux and K+ influx via Na+/K+ ATPase pump)
Absolute Refractory period
Phase 0-2 & early part of 3, time period where the cell can not depolarize agin
Cardiac myocytes
Fast response
Class I agents works on which phase?
Works on phase 0
Class II and IV works on which phase?
Phase 2
Class III and I A works
Phase 3
Phase 2 drugs are classes
Acts on Class II and IV
Phase 3 drugs are classes
Acts on Class III and IA
****Cardiac nodal tissue’s (SA & AV node)
depolarization is largely controlled by
Ca2+ channel current and are referred to as slow response tissue
Phases of action potential of cardiac
pacemaker (nodal) cells
Phase 4 spontaneous depolarization to threshold (also called diastolic depolarization or pacemaker potential) – diffusion of K+ out of cell decreases progressively and diffusion of Na+ into cell increases progressively. During the last 1/3rd of phase 4, Ca2+ ions begin to diffuse into the cell • Phase 0 slow depolarization Ca2+ diffuses into the cell and slight Na+ influx • Phase 3 repolarization –K+ diffuses out of the cell • Pacemaker cells are slow response tissue
Are the sodium channels the same for the pacemaker nodal cells?
NO
PACEMAKER OF MUSCLE CELLS
SLOW RESPONSE TISSUE WHEN COMPARED TO MYOCYTE CELLS (BECAUSE THEY DON’T CONDUCT ion movements as fast)
Cardiac antidysrhythmic drugs produce their pharmacologic effects by:
blocking the passage of ions across Na+, K+, and/or Ca2+ ion channels present in the heart
Drugs may decrease automaticity (meaning these agents will slow “automatic” rhythms) by altering any of the 4
determinants of the spontaneous pacemaker discharge
- Decrease phase 4 depolarization
- Increase threshold potential
- Increase maximum diastolic potential
- Increase action potential duration
*****Vaughan-Williams Classification of
Antiarrhythmic Drugs
- Class I- Na+ Channel Blockers (fast Na only)
- Class II- Beta-adrenergic Blockers
- Class III - K+ Channel Blockers
- Class IV - Ca2+ Channel Blockers (only VERAPAMIL and DILTIAZEM
***Class IA Names
– Quinidine (PDQ)
– Procainamide
– Disopyramide
**Class II Names
Esmolol (MEPA)
Acebutalol,
Propranolol,
Metoprolol
*** Class III Names
- Amiodarone (ADIDS) – Dronedarone – Dofetilide – Ibutilide – Sotalol
***Class IB Names
– Lidocaine (LPM)
– Mexiletine
– Phenytoin
***Class IC Names
– Flecainide (FP)
– Propafenone
***Class IV Names
– Verapamil
– Diltiazem
The following agents are also anti-arrhythmic drugs but do
not fit into the Vaughan-Williams Classification system
Digoxin (DAMI)
– Adenosine
– Magnesium
– Ivabradine (Corlanor)
Class I agents are classified as Na+ channel blockers (fast Na+ channels)
• Class I anti-arrhythmic drugs bind to and block/inhibit fast Na+ channels that are responsible for the rapid depolarization (phase 0) in non-nodal tissue, which results in the following:
– Inhibits depolarization by reducing the rate of rise of phase 0 of the action potential, also known as Vmax (aka: Decreases phase 0 of the fast action potential) and decreases the amplitude of the cardiac action potential
– Slows conduction velocity in atria, ventricles and His-Purkinje fibers (non-nodal tissue)
– Decreases automaticity
Antidysrhythmic effects are due to blockade of the responses
of beta-adrenergic receptors in the heart to SNS stimulation, as
well as the effects of circulating catecholamines
- Class II drugs are beta-adrenergic antagonists
* Every beta-blocker on the market is a Class II agent!
Class II mechanism of action (NODAL)
Decrease automaticity by decreasing the rate of phase 4 spontaneous depolarization of SA node.
Decrease AV nodal conduction velocity
Negative chronotrophic
Negative Inotrope (decrease phase II of non-nodal tissue
Can produce AV block
Class III agents are classified as
K+ channel blockers.
Class III antiarrhytmic drugs bind to and blcok
K+ ion channels which prolong repolarization (phase III) by :
prolonging the duration of the cardiac action potential and the effective refractory period (ERP) (prolong refractoriness) of atrial and ventricular myocytes
Class IV: Mechanism of action (MYOCYTES)
Verapamil and diltiazem act by inhbiting the influx of Ca2ions acrross slow L-type voltage-gated ca2+ channels of CARDIAR MYOCYTES, SA and AV nodal
So they are NEGATIVE INOTROPE.
NEVER GIVEN TO Heart failure with Decreased EF (HfrEF)
Class IV agents increase the (in NODAL)
Threshold voltage resulting in decreased amount of Ca2+ entry into the nodal cell.
Took longer for phase IV to reach
**Class IV mechanism of action (NODAL)
Inhibiting calcium entry into the cardiac NODAL tissue cells results in :
- Decreased rate of spontaneous phase 4 depolarization
- Decreased SA and AV node automaticity
- Decreased Conduction velocity through AV node (negative dromotrope)–>Prolonged PR
- Decrease HR
- Increased Refractory Period.
Class IV agents : effects of only those 2 drugs, but NOT a class IV mechanism
Inhibits calcium entry into vascular smooth muscle tissue which results in relaxation of vascular smooth muscle of coronary arteries and systemic arteries (HYPOTENSION mechanism)
Useful in reentrant tachycardia that arise from or use the SA and AV nodes
Verapamil and Diltiazem
Class I - Na+ Channel Blockers
Another difference:
All class I agents have a predominant affinity for a particular state of the Na + channels when they block the Na+ channel, which influences its clinical effects - Affinity during activation and/or inactivation.
All Class I agents possess a
property called rate dependence (used dependence), their sodium channels are best at fast HR
Na+ Channel blockade and slowing of conduction by the drugs is
GREATEST at fast heart rates and least during Bradycardia.
Sodium channel blockers work better
when HR is higher.
Which category Class IA agents:
All class IA In addition to blocking fast Na+ channels ALSO block K+ channels in the heart.
They have Class I and Class III effects.
Non-nodal tissues
All class IA agents have proarrythmic agents: By blocking \_\_\_\_\_\_\_\_they do what? putting patient at risk for \_\_\_\_\_\_\_ Significant \_\_\_\_\_\_ \_\_\_\_\_
blocking potassium Channels( prolonged QT ) Increase Torsades de pointes
Significant negative inotropes.
Class IA drugs are broad spectrum agentst and are effective for both
SVTs and Vtach
**Class ____are rarely used for anesthesia due to ______ ______
Profound HYPOTENSION
Quinidine Class IA
is a class IA agents that blocks Na+ channels in the "open' state only AND also blocks K+ currents/channels Posess alpha adrenergic ANTAGONIST, anticholinergic effecfs and ANTIMALARIAL EFFECTS
Clinical use of Quinidine first slide not important.
Last resorts for Atrial or ventricular arrhythmias
Additional pharmacological effects
Prolong QRS and *****QT interval
Shortened PR
Metabolism of Quinidine
metabolize in liver via CYP3A4
active metabolites
HIGHLY PROTEIN BIND to ALBUMIN80-90
20% Kidney as unchanged drug.
Avoid quinidine in
HF patients
Quinidine SIDE EFFECTS
*****Diarrhea (most common) Nausea Syncope HYPOTENSION REFLEX TACHYCARDIA
Quinidine Immunological reactions
LUPUS-LIKE REACTIONS
Cinchonism with ________include
Quinidine; tinnitus, headache, decreased hearing acuity, blurring vision
*****Quinidine -Drug interactions
**Potentiates/ACCENTUATES non-depolarizing and depolarizing neuromuscular blockers.
Quinidine increases ______serum concentration.
digoxin
Decrease quinidine concentration
CYP 3A4 inducers
INcrease quinidine concentration
CYP3A4 inhibitors
Quinidine has a ______adrenergic antagonists which can produce _______-
alpha; Vasodilation.
PROCAINAMIDE is a ________ and it
Class IA ; blocks Na+ channels in the open state and ALSO blocks K+ current/channels, and has a VERY WEAK anticholinergic effects. Same electrophysiologic
Clinical use of Procainamide
Does same as quinidine except does not have ANTAGONISTIC PROPERTIES
PROCAINAMIDE Dosing
In urgent situation for VTACH conversion
100mg IV every 5 minutes until 15mg/kg given, the arrhythmia ceases OR the QRS widens >50%
Procainamide Afib concersion
Gram IV OVER 30 minutes, then 2mg/min
Procainamide is eliminated by both
Renal metabolism and
hepatic metabolism
**Acetylation of procainamide produces an
***active metabolite called NAPA (N-Acetyl procainamide)
The activity of N-actetyl transferase enzyme is
determined genetically, patients may either have
-normal activity or reduced activity (slow acetylators) or increased activity (Fast acetylators)
Procainamide clearance required_______
required adequate kidney
Both procainamie and NAPA are excreted via the kidneys necessating
dosage adjustements in renal failure patietn.
NAPA
has class III effects and prolonged the half life.
No oral dose of
Procainamide
**BIGGEST CONCERN FOR ANESTHESIA as far as procainamide
*****HYPOTENSION
Rapid IV administration of procainamide can lead to hypotension which limits
the use of this agents during general anesthesia
– Hypotension is due to direct myocardial depressive effect
– Never give as a rapid IV bolus
Procainamide not given in patients with
heart block –> can lead to systole
Oral dosage form of procainamide
NO LONGER AVAILABLE in the USA.